The present inventions are related to systems and methods for transferring information to and from a storage medium, and more particularly to calibration systems and methods for accurately positioning a sensor in relation to a storage medium.
Various electronic storage media are accessed through use of a read/write head assembly that is positioned in relation to the storage medium. The read/write head assembly is supported by a head actuator, and is operable to read information from the storage medium and to write information to the storage medium. The distance between the read/write head assembly and the storage medium is typically referred to as the fly height. Control of the fly height is critical to proper operation of a storage system. In particular, increasing the distance between the read/write head assembly and the storage medium typically results in an increase in inter symbol interference. Where inter symbol interference becomes unacceptably high, it may become impossible to credibly read the information originally written to the storage medium. In contrast, a fly height that is too small can result in excess wear on the read/write head assembly and/or a premature destruction of the storage device.
In a typical storage device, fly height is set to operate in a predetermined range. During operation, the fly height is periodically measured to assure that it remains in the predetermined region. A variety of approaches for measuring fly height have been developed including optical interference, spectrum analysis of a read signal waveform, and measuring a pulse width value of the read signal. Such approaches in general provide a reasonable estimate of fly height, however, they are susceptible to various errors. In some cases, fly height has been measured by utilizing harmonic measurements based upon periodic data patterns written to the user data regions of a storage medium. Such approaches are problematic as they reduce the amount of storage that may be maintained on a given storage medium.
In some cases, fly height has been measured by utilizing harmonic measurements based upon periodic data patterns written to or available in the servo data regions of a storage medium. These approaches facilitate format saving since harmonic sensing is done based on data already available in the servo data region and no extra patterns need to be written to the servo region for harmonic sensing purpose. However, the harmonic measurements made from this are prone to errors contributed by variations in electronic circuits through which the servo signal pass through before harmonic computations are done. These changes in circuits are caused by changes in environmental conditions such as temperature, voltage, or altitude.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced calibration systems and methods for positioning a sensor in relation to a storage medium using servo data based harmonics sensing.